1. Technical Field
This invention relates to a cylindrical paraboloid weather cover for a horn reflector antenna, and more particularly, to contouring the weather cover in such a manner so that microwave reflections from the weather cover are focused onto a microwave absorber-covered linear section inside the antenna, thereby reducing the sidelobes generated by weather cover reflections.
2. Description of the Prior Art
In the past, to prevent the entry of rain, snow, and other various foreign bodies into the aperture of a horn reflector antenna and hence flowing down the waveguide transmission line, the aperture was covered by a flat piece of glass fiber fabric. The application of the weather cover was highly successful in excluding the elements, however, the reflections from the flat weather cover contributed to the sidelobe problem of horn reflector antennas. Parabolic designs have been considered, but only in conjunction with microwave dish antenna configurations, in which weather covers are referred to as radomes.
One example of this parabolic design is disclosed in U.S. Pat. No. 3,740,755 issued to R. J. Grenzeback on June 19, 1973. In this case, the antenna arrangement comprises a parabolic reflector with a confocal parabolic radome. The coincident foci of the reflector and radome causes reflections from the latter to be incident upon the reflector in the same direction as the energy directly incident thereon from the feed.
The use of a dielectric or microwave absorbing material in conjunction with radomes is also well-known in the prior art, and is discussed in the article "Gain Enhancement of Microwave Antennas by Dielectric-Filled Radomes" by J. R. James, et al in Proceedings of the IEE, Vol. 122, No. 12, December 1975 at pages 1353-1358. This article relates the performance of a microwave antenna which comprises a radome packed with dielectric material. Originally, the radome was packed to strengthen its aerodynamic profile. Using a simplified model based on rectangular geometry, it can be shown that such packing actually increases the gain of the antenna system.
The problem remaining in the prior art is to provide a method for suppressing the reflection sidelobes attributed to the use of weather covers in conjunction with horn reflector antennas.